Method for the Production of Forged Steel for Weapons Subject to Heavy Stresses, Barrel Blanks and Thus-Equipped Weapon

ABSTRACT

It is proposed to make a change to the barrel material and also its constituent proportions and to undertake a production method which is already known from the large caliber barrel but which is specially adapted for medium caliber barrels. A barrel is created which is now made from a NiCrMoV steel blank which as an ingot was remelted in the ESR (electro-slag remelting) process before forging and the forged bars were quenched and tempered in a liquid quenching and tempering process. A barrel for a machine gun is thus disclosed which has the quality/characteristics of a large caliber barrel.

Process for the production of forged steel for weapons subject to heavystresses, barrel blanks and a weapon equipped therewith

The invention relates to a process for the production of gun barrelblanks for machine guns in the caliber. range, in particular, of 25-50mm.

Standard materials for machine guns subject to such heavy loading areheat-resistant CrMoV-alloyed heat-treated steels, such as the steel 32CrMoV 12-10, material No. 1.7765 in accordance with “Stahl-Eisen-Liste”(Steel/iron list) (Verlag Stahleisen, Dusseldorf) for 30 mm machineguns, which has been customary to date. This material satisfies thedemands for high yield strength (min. 950 N/mm²) together with a highheat resistance up to 4500 (min. 550 N/mm²) to achieve a sufficientlylong service life of the barrels.

In the context of improving performance, improving quality andincreasing the standard of safety, even more stringent demands are beingplaced on the material and on the quality of the forged blank. Theseresult from the features of development such as increased gas pressureloading by new munitions concepts, the inducing of residual stresses byhydraulically expanding the inner wall of the barrel in order toincrease the fatigue strength, more stringent demands on the aimingaccuracy as a result of increased muzzle velocities of the newmunitions, the ability of the chromium layer to be readilychromium-plated and to be durable during firing, and an increasedpotential to protect against brittle fracture in the temperature rangeof −50 to +80° C.

Although the steel used, grade 32 CrMoV 12-10, has a sufficientpotential for satisfying the demands regarding strength which are made,for example, on a new 30 mm machine gun, it fails to achieve the targetsregarding the required degree of toughness. Further inadequacies of theconventional material include the low degree of purity in the case ofopen melting and the pronounced tendency of the barrel to distort owingto directional loading during firing.

DE 101 11 304 C2 discloses a process for the production of barrels forheavy cannons. The heat-treated steel produced in different compositionsis hardened and tempered, subsequently bored and then finished. Theresult of this is that a maximum degree of straightness is achieved, andthe quality of the barrels produced in this way is superior to that ofconventionally straightened barrels. It is known, however, thatdifferent demands are placed on large caliber blanks than on mediumcaliber blanks. Medium caliber weapons are exposed to a higher firingrate than large caliber weapons.

On the basis of this process, the object of the invention is to specifya process for the production of barrels in the medium caliber range witha relatively high firing rate and also a corresponding barrel whichsatisfies even the latest demands.

This object is achieved by the features of claims 1, 7 and 10.Advantageous refinements are specified in the dependent claims.

The invention is based on the concept, in a manner similar to thebarrels in the large caliber range, of providing a change of the barrelmaterial as well as its constituent proportions and also a productionprocess which is already known from the large caliber barrel but isspecially adapted to medium caliber barrels. Although it must be takeninto account that a barrel for medium caliber use is exposed to higherpermanent loading during functional use than is known for large caliberuse, an additional requirement in further considerations of these mediumcaliber weapons is that the so-called opening shot of a medium caliberor rapid-fire weapon should, in practice, produce the required hitaccuracy. When selecting the barrel material, it should therefore alsobe taken into account that the weapon barrel is to be designed both forsingle rounds and for a high firing rate. It is correspondingly proposedthat the novel material concept coming into effect should be developedon the basis of an electroslag remelted NiCrMoV steel which has beenheat treated in a suspending/rotating manner, which therefore evenlargely corresponds to the steel 35NiCrMoV 12-5, material No. 1.6959which is known for large caliber weapons. To date, this steel has notbeen used for high-firing rate machine guns owing, in particular, to thestringent demands regarding heat resistance which are placed on thebarrel.

In practice, it has also been shown that this steel, in modified form,corresponds to the required degrees of heat resistance in conjunctionwith increased resistance to heat treatment. At the same time, themartensitic microstructure of this novel NiCrMoV steel means that it hasa considerably increased toughness potential compared to the bainiticCrMoV steel. The safety requirements demanded can be met down totemperatures as low as −50° C. owing to the high degree of toughness.

The barrel produced by the novel process is distinguished in that ahigher yield strength is achieved (approx. 1050 N/mm²). Furthermore, thebarrel has a sufficiently high notched impact strength and fracturetoughness down to −50° C. and has a sufficiently high heat resistance upto +50° C. The high degree of purity (K₀ value max. approx. 12) is afurther advantage. The production of the gun barrel blank takes placewithout residual straightening stresses, i.e. the heat treatment takesplace without subsequent straightening operation.

A process for the production of gun barrel blanks for machine guns inthe preferred caliber range of between 25-50 mm is distinguished by thefollowing composition:

-   0.25-0.50% carbon

max. 0.60% silicon

max. 1.00% manganese

max. 0.010% phosphorus

max. 0.010% sulfur

1.00-1.40% chromium

2.00-4.00% nickel

0.30-0.70% molybdenum

0.10-0.30% vanadium

max. 0.05% aluminum and

remainder iron and conventional (unavoidable) impurities,

wherein the blanks are produced from remelted steel or from steel whichis melted in the open and has a high degree of purity.

The following composition of the heat-treated steel has proved to bepreferred:

0.30-0.35% carbon

max. 0.40% silicon

0.4-0.70% manganese

max. 0.005% phosphorus

max. 0.005% sulfur

1.00-1.40% chromium

2.50-3.3% nickel

0.50-0.60% molybdenum

0.10-0.20% vanadium

max. 0.03% aluminum and

remainder iron and conventional impurities.

In order to ensure that the high demands placed on the degree of purityare met, the steel is preferably remelted in the cast state using theESR (electroslag remelting) process. The high homogeneity of themicrostructure which is associated therewith (as a result of improvedsegregation) is the basis for the low-distortion heat treatment which iscarried out in the vertical dipping direction by means of oil or watercooling. The blanks which are forged as a bar are tempered in thisprocess by means of the vertical liquid heat-treating process to yieldstrengths of >1000 N/mm². During the heat treatment, the barspermanently rotate about their axis or are permanently turnedmechanically about their axis. Machining takes place without priorstraightening operation.

In addition, the novel steel for a medium caliber barrel makes itpossible to achieve improved autofrettage (the barrel becomes moreheat-resistant—up to 500° C.). The barrel itself is thereby able to moreefficiently absorb residual stresses, which means that the ability ofthe barrel to absorb pressure is increased.

1-14. (canceled)
 15. A process for producing gun barrel blanks formachine guns, comprising the step of combining 0.25-0.50% carbon, max.0.60% silicon, max. 1.00% manganese, max. 0.010% phosphorus, max. 0.010%sulfur, 1.00-1.40% chromium, 2.00-4.00% nickel, 0.30-0.70% molybdenum,0.10-0.30% vanadium, max. 0.05% aluminum, and remainder iron andconventional impurities, all percentages are by weight.
 16. The processaccording to claim 15, including 0.30-0.35% carbon, max. 0.40% silicon,0.4-0.70% manganese, max. 0.005% phosphorus, max. 0.005% sulfur,1.00-1.40% chromium, 2.50-3.3% nickel, 0.50-0.60% molybdenum, 0.10-0.20%vanadium, max. 0.03% aluminum, and remainder iron and conventionalimpurities.
 17. The process according to claim 15, further includingproducing the blanks from remelted steel or from steel which is meltedin the open and has a high degree of purity.
 18. The process accordingto claim 17, including remelting the ingots using an ESR (electroslagremelting) process prior to forging.
 19. The process according to claim17, including producing forged bars and heat-treating the forged bars ina liquid heating-treating process.
 20. The process according to claim19, including heat-treating the forged bars vertically in oil or water.21. The process according to claim 19, wherein during heat treatment,the bars permanently rotate about their axis or are permanently turnedmechanically about their axis.
 22. A blank for a machine gun barrel,comprising a heat-treated steel, including: 0.25-0.50% carbon; max.0.60% silicon; max. 1.00% manganese; max. 0.010% phosphorus; max. 0.010%sulfur; 1.00-1.40% chromium; 2.00-4.00% nickel; 0.30-0.70% molybdenum;0.10-0.30% vanadium; max. 0.05% aluminum; and remainder iron andconventional impurities as NiCrMoV steel.
 23. The blank according claim23, wherein the heat-treated steel includes: 0.30-0.35% carbon; max.0.40% silicon; 0.4-0.70% manganese; max. 0.005% phosphorus; max. 0.005%sulfur; 1.00-1.40% chromium; 2.50-3.3% nickel; 0.50-0.60% molybdenum;0.10-0.20% vanadium; max. 0.03% aluminum; and remainder iron andconventional impurities as NiCrMoV steel.
 24. The blank as according toclaim 22, wherein the steel is remelted as an ingot using an ESR processprior to forging and forged bars are heat-treated in a liquidheat-treating process.
 25. A machine gun having at least one barrelconsisting of NiCrMoV steel.
 26. The machine gun according to claim 25,wherein the NiCrMoV steel is remelted using an ESR process prior toforging and the forged bars are heat-treated in a liquid heat-treatingprocess.
 27. The machine gun according to claim 25, wherein the barrelis comprised of a NiCrMoV steel including: 0.25-0.50% carbon; max. 0.60%silicon; max. 1.00% manganese; max. 0.010% phosphorus; max. 0.010%sulfur; 1.00-1.40% chromium; 2.00-4.00% nickel; 0.30-0.70% molybdenum;0.10-0.30% vanadium; max. 0.05% aluminum; and remainder iron andconventional impurities.
 28. The machine gun according to claim 27,wherein the barrel is comprised of a NiCrMoV steel including: 0.30-0.35%carbon; max. 0.40% silicon; 0.4-0.70% manganese; max. 0.005% phosphorus;max. 0.005% sulfur; 1.00-1.40% chromium; 2.50-3.3% nickel; 0.50-0.60%molybdenum; 0.10-0.20% vanadium; max. 0.03% aluminum; and remainder ironand conventional impurities.
 29. The machine gun according to claim 25,wherein the barrel has quality/properties that match quality/propertiesof a large caliber barrel.